1. Field Of The Invention
This invention relates to a novel use of ultrasonic energy to cut fibrous materials made of cellulose or its derivatives, such as paper; and to useful devices resulting from the novel method. More particularly, the invention relates to a method for cutting paper where the paper is first chemically modified, eg. by treating it with an oxidizing agent, and then is subjected to ultrasonic energy directed along a predetermined path or line.
2. Background
A. The Chemistry Of Cellulose
Under controlled conditions oxidation has been used to decrease the chain length of the cellulose polymer. For example, standard chemistry texts such as Morrison and Boyd, Organic Chemistry, 4th Ed. (1983), pages 523 and 1113, teach that oxidation of 1,2-diols by periodic acid can reduce the chain length of the cellulose polymer from 1,500 or more glucose units to about 1,000 glucose units.
Paper consists of sheet materials that are composed of bonded small discrete fibers. Greater than 95% of this sheet material is fibrous and more than 90% of the material originates from wood. Of the remaining 10% of the sheet material, half comes from non wood fibers such as cotton or flax (which are cellulosic in nature) and the other half is filler or pigment. The art of papermaking and the use of papermaking additives is disclosed in Kirk-Othmer, Encyclopedia of Chemical Technology, 3d Vol. 16 (1981), pp. 768-802 and 803-821, the teachings of which are incorporated herein. In paper making, chemical oxidative treatment may be used as a bleaching treatment to improve the brightness of the paper.
B. Ultrasound
Ultrasonic energy is typically produced by a piezoelectric transducer driven by a power supply. The transducers produce a repeating wave and can be coupled to the load (object being treated) either directly or through resonant members. Kirk Othmer, Encyclopedia of Chemical Technology, 3d Ed., Vol. 83, (1983) pages 462-479, incorporated herein by reference, presents a teaching of the workings and applications of ultrasonics. Basically, ultrasound produces compressional waves in the load. The propagation and absorption of these waves depend on the elastic and dissipative characteristics of the medium. In liquids and gases, only compressional waves are possible. In solids, however, the compressional waves can give rise to other vibrational modes such as shear, torsion or flexure.
Although ultrasound has a number of applications, its use in plastics welding is most relevant to the present invention. U.S. Pat. No. 3,666,599 (Obeda) discloses the use of a rotating anvil in an ultrasonic seaming apparatus ("welder") to form a seam between two layers of "textile fabrics which contain thermoplastic fibers." The rotating anvil which opposes the ultrasonic resonator, provides continuous zigzag and intermittent welds analogous to the stitching of a sewing machine.
U.S. Pat. No. 4,244,762 (Holson) discloses the use of ultrasonic energy to produce a plastic photographic album page comprising a fibrous material, such as paper, laminated between two sheets of ultrasonically weldable plastic. The Holson '762 lamination technique requires that enough energy be generated at the point of the weld to vaporize the paper. Thus Holson employs a discontinuous weld in order to permit the vaporized paper to vent. Further, Holson teaches that discontinuous stitching permits the fibrous lamina to be captivated without weakening its mechanical strength.
C. Devices
There are numerous devices on the market today employing plastic housings around fibrous materials. The diagnostic market alone abounds with such devices, used for example in chromatographic analyses. Many of these devices, however, are sophisticated and costly to manufacture. Simple devices such as dip sticks or paper chromatographs are available, but are generally directed towards simple tests, and are usually qualitative or semi-quantitative, at best. They also encounter problems with contamination from external sources, and evaporation of reagent and sample fluids.
More sophisticated devices avoid these problems by employing a housing. Examples of such housings can be found in Wright in U.S. Pat. No. 3,915,647; Tom, et al., U.S. Pat. No. 4,366,241; Valkirs et al., U.S. Pat. Nos. 4,632,901 and 4,727,019; and others.
Typically, housings known in the prior art have been molded of two components, the components being manually assembled to house the enclosed materials. Assembly may require special adhesives and adds to the cost of manufacture. Moreover, adhesives can contribute to instability. Often adhesives will give off volatile compounds (eg. ketones) which are detrimental to reagent stability.